We tend not to think of turtles as predators, and that their ingenious arsenal includes mainly defensive designs, but new research suggests turtles’ ability to stick out and retract their neck was originally to grab prey, not to protect themselves.

The term “stick your neck out”, the idea of putting yourself out there even though it makes you vulnerable, comes from the risk a turtle takes every time it literally sticks its neck out. But ancient turtles may not have been as timid as we thought.

Scientists from the Jurassica Museum in Switzerland re-examined a fossilized turtle thought to have lived 150 million years ago. They found that it had the ability to partially withdraw its head into its shell, but not completely, suggesting the primary mechanism was to allow the head to dart forward, catching quick-moving prey. The ability to completely retract was probably a secondary benefit that evolved later. Their study is published in the journal Scientific Reports.

The two modern monophyletic groups of turtles (descending from a common evolutionary ancestor), Pleurodires and Cryptodires, both independently evolved neck retraction mechanisms, sideways and backwards, respectively. These are assumed to be protective, defensive mechanisms.

The researchers studied the fossil of a turtle from the Late Jurassic, called Platychelys oberndorferi, that was found in Switzerland in the 19th century, but not examined thoroughly. It turns out P. oberndorferi had morphological and functional similarities to modern cryptodires in that it could partially withdraw its neck into its shell.

But the fossil revealed it would not have been able to completely retract its neck, leading the researchers to conclude that retracting backwards was not its primary mechanism, and that evolved independently later. Instead, the ability allowed the neck to shoot forward, described by the authors as a "fast ram feeder".

“Since head and neck retraction was only partial in P. oberndorferi, we suggest that vertical neck retraction primarily evolved in this taxon to enable fast forward projection of the head and improve capture of darting prey,” they wrote.

They concluded that several of the anatomical features suggest P. oberndorferi was an ambush predator, either ramming its head forward to snatch prey or sucking it into its mouth, reminiscent of modern snapping turtles.  

The researchers hope to test their theory further by studying the mechanism that controls the heads of modern turtles during feeding.